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What impact does ethanol have in the operation of the wastewater treatment plant?

Q: I'm looking for information regarding refineries' experiences handling ethanol-gasoline vapors from truck loading racks in their flare system. Also, the impact ethanol has in the operation of the wastewater treatment plant. In some systems, these vapors will mix with water (in headers, FGR units, Flare KO drums, sour water stripping units, etc.) and will end up in wastewater units. What steps have been taken to manage this situation?

A:

The answer to the question is that the data are extremely hard to find. I don't know of any sources.  I suspect that the reason that there is not any discussion out there is because it is a non-problem.

Ethanol is miscible with water to 100%.  As such, it has a slight increase in the organic component of the demand, or the BOD, or COD, however you want to measure it. In a stripper the ethanol will be relatively dilute.  One gram of ethanol has a theoretical Oxygen Demand of 192/180 gm of Oxygen or about 1.05 gm/ gm. So while ethanol imposes a load on a wastewater treatment plant, in terms of increasing oxygen demand, it really does little else.  The bacteria in the wastewater treatment plant will enjoy an ethanol diet as long as it is not too strong (too strong in this case is in the 3%  or more range).  Verschuren's book on Environmental Data on Organic Chemicals indicates that toxicity to many organic organisms doesn't start until approximately 32,000 mg/l (3.2%). In a wastewater treatment system about 40% of it is destroyed in 24 hours.

So, don't worry about the effect of ethanol unless it is a really concentrated stream, and then you may have other problems.

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